The present invention relates to improvement of performance of loudspeakers in general and specifically to stabilization of loudspeakers operating within the mid to high-frequency range and having a magnet system and voice coil connected to a diaphragm.
Referring to Prior Art FIG. 1a, in a conventional tweeter-type, sometimes referred to as a dome type, loudspeaker there is a half-circular (in cross-section) outer-ring diaphragm portion 2 and a semi-circular (in cross-section) inner-dome diaphragm portion 4, residing within the diameter of the outer ring. Attachment location 12, 20 illustrates how the outer-ring diaphragm portion 2 is connected, as with gluing for example, near the outer circumference of the outer ring to the diaphragm chassis 5. Attachment location 14, 18 illustrates where the outer-ring diaphragm portion 2 is interconnected, as with gluing for example, near the inner circumference of the outer-ring portion 2 and near the outer circumference of inner-dome diaphragm portion 4 by means of a cylindrical, annular armature 22 upon which is wound the voice coil winding 24 and which are free to vibrate between a top plate 28 and yoke 30 of the speaker. As is conventional, the top plate 28 and yoke 30 have a magnet 32 between them in sandwich construction as shown. Magnetic energy is transferred by the top plate 28 and yoke 30 from the magnet 32 to the voice coil gap between the top plate and yoke. Attachment locations 12, 14, 18, 20 of the dome-type loudspeaker diaphragm have lied in a single plane.
Similarly, as shown in FIG. 1b, the attachment points 12, 14, 16, 18, 20 of another conventional ring-radiator type loudspeaker diaphragm have lied in a single plane, additional attachment location 16 serving to connect a center portion of diaphragm portion 4 with a center post 26. Thus, FIG. 1b illustrates another type of tweeter loudspeaker, wherein the central diaphragm portion 4 includes an inner ring and not a dome as shown in FIG. 1a. 
As the described conventional speakers' diaphragm portions 2, 4 are operated through their range of motion, the voice coil 24 is motivated along a typically, and preferably, linear path by fluctuations in the magnetic field representing the sound signals being transduced and to which the voice coil 24 is exposed. However, traditional limitations of speaker systems, such as magnetic flux variations in the permanent magnet 32, variances in gap widths between the top magnetic plate 28 and the yoke 30, and electronic magnetic flux variations in the voice coil 24 due to such things as manufacturing imperfections in voice coil windings and their materials, have all resulted in an imbalanced application of force to the diaphragm portions 2, 4. All of these factors and others have contributed to the diaphragm moving and tilting off of its axial center, especially at resonant frequencies where the speaker presents the greatest impedance to power applied to the voice coil. This condition, sometimes referred to as rocking, distorts speaker output. This rocking condition is illustrated in FIGS. 2a-2c, wherein FIG. 2a shows the diaphragm portions 2, 4 and voice coil 24 at rest, FIG. 2b shows the diaphragm portions 2, 4 and voice coil 24 at full excursion, their furthest travel distance during operation, and FIG. 2c shows the diaphragm portions 2, 4 and voice coil 24 in a rocked condition most easily seen in that the armature 22 and voice coil 24 are shown slightly tilted between the top plate 28 and the yoke 30. It will be appreciated by those of ordinary skill in the art that the rocked condition shown in FIG. 2c, and the full excursion of FIG. 2b, are exaggerated to allow visual illustration of these conditions of full excursion and rocking, whereas actual excursion and rocking vibrations are on a much smaller scale not readily visible to the human eye.
It is largely accepted in the industry that rocking contributes to distortion in speaker output, especially at the speaker's fundamental resonant frequency. As design and manufacturing improvements yield higher performing speakers having tighter tolerances between the yoke 30 and top plate 28, severe rocking, most likely to occur in the lower frequency ranges of a mid to high range dome-type speaker, becomes more intolerable, as it would degrade speaker performance and speaker life.
Referring to FIG. 1b, though there is an attachment of the inner ring of the diaphragm at location or point 16, due to the planar nature of the attachment, rocking still persists with this speaker design. FIG. 2d illustrates this type of speaker of FIG. 1b at rest, and FIG. 2e shows, again in exaggerated condition for purposes of illustration, the loudspeaker of FIG. 1b in an out-of-axis, rocked, condition.
While casual listeners may not notice distortion resulting from rocking, any person who is especially interested in high-fidelity sound reproduction finds technical measurements to be important and decisive. Further, there is an increasing desire in speaker design and manufacturing circles to improve low frequency response of tweeter and mid-range speakers especially at resonant frequencies. Alternatively, speaker providers desire lower resonant frequencies which increase the frequency range in which a speaker is available to operate without overcoming severe impedance abnormalities at resonant frequency. Increasing the size of the annular ring radiator portion of a dome-type speaker to accomplish such lower frequency response has exacerbated rocking in such speakers.